Surface-active materials (surfactants) are used in fracturing operations to promote well cleanup following the use of water-based fracturing fluids. These products are generally blends of surfactants in solvent systems that keep the surfactants stable in storage, but are easily pumped and diluted in frac fluids to become active. Performance of the surface-active materials is generally based on cost to provide reduction in interfacial tension and reduction in contact angle, both which facilitate the removal of water from a porous media (for example, a proppant packed fracture) with mixtures of gas or oil by preventing or breaking emulsion formation. These products are mostly marketed as commodity materials and are very price sensitive.
Prior technology calls for adding a minimum concentration of one or more surface-active materials (surfactants) to the one or more fluids used in fracturing of a treatment zone required to cause the desired effect on cleanup throughout the entire fracturing treatment. Large volume fracturing treatments can require large volume of surfactant-based products to promote well cleanup.
In low permeability fracturing such as shale fractures, there is little fluid lost to the formation so that nearly all the fluid goes to creating fractures. As fluid is injected into a fracture to extend the fracture, the leading front of the fracture will be greatly reduced in the concentration of surfactant that is in the fluid at that point owing to the fact that surfactants tend to adsorb to the fracture face. Therefore, the leading edge of the fracturing fluid contains an inadequate amount of surfactant to affect the desired surface energies. In addition, any fluid that does leak off into the formation will not contain sufficient surfactant. To combat this problem, higher surfactant concentrations are used than are actually required.